PLATELET ACTIVITY AND SALT SENSITIVITY IN THE PATHOGENESIS OF SYSTEMIC (ESSENTIAL) HYPERTENSION IN BLACK-AFRICANS

Black essential hypertensive patients with a mean arterial pressure of 125+/-3 mm Hg (mean +/- SEM), and age and sex matched normotensive subjects with a mean arterial pressure of 89+/-2 mm Hg were studied under baseline conditions, after five days of salt restriction and after five days of salt loading. Salt sensitivity was defined as an increase of mean blood pressure exceeding 5% when progressing from low to high sodium intake. In vitro platelet responsiveness was assessed by aggregometry, and in vitro platelet activity by estimation of beta-thromboglobulin (BTG) in plasma and thromboxane B2 (TXB2) excretion rate. Salt sensitivity was present in 66% of hypertensive and 55% of the normotensive subjects. An increased platelet aggregability to ADP (25%), to epinephrine (34%) and to collagen (12%) was found in parallel with an increased in vivo platelet activity (BTG increased by 55% and TXB2 by 18%) in the hypertensives. All changes were significantly exaggerated in the salt sensitive as compared to salt resistant hypertensive patients.